# The Naked Scientists Forum

### Author Topic: How does a Newton's Cradle work?  (Read 3552 times)

#### Joe Dweck

• Guest
##### How does a Newton's Cradle work?
« on: 13/09/2008 11:51:15 »
Joe Dweck asked the Naked Scientists:

Love the show, I catch it on podcasts.

Ya know the Newton's Cradle desktop toy with steel balls? When you pull two away, they snap back and two bounce out the other way. I understand conservation of energy, but why doesn't one come out wih twice the energy?

What do you think?

#### syhprum

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##### How does a Newton's Cradle work?
« Reply #1 on: 13/09/2008 16:56:14 »
This has been discussed many times on this board, I am sure a reference can be found.

#### paul.fr

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##### How does a Newton's Cradle work?
« Reply #2 on: 13/09/2008 23:08:07 »

#### Bored chemist

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##### How does a Newton's Cradle work?
« Reply #3 on: 14/09/2008 19:02:40 »
"why doesn't one come out wih twice the energy?"
Essentially, because both momentum and energy have to be conserved.

#### lyner

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##### How does a Newton's Cradle work?
« Reply #4 on: 14/09/2008 21:51:39 »
It all boils down to what happens when a single ball hits an identical ball - if there is no energy loss, the parting speed will be the same as the speed of approach - they will 'exchange velocities. Total momentum and energy remain the same. You can extend this to a whole row of balls.
We did the sums in sixth form A level mechanics  and it all came out with some very simple calculations.

You can end up with an increase in speed when you have different masses and with both objects moving towards each other - e.g firing a ball bearing at the front of an express locomotive, when the ball bearing will bounce back with (almost) the sum of the two initial speeds.

#### Don_1

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• A stupid comment for every occasion.
##### How does a Newton's Cradle work?
« Reply #5 on: 17/09/2008 07:25:47 »
Here is a simple explanation, by smiley :

#### blakestyger

• Guest
##### How does a Newton's Cradle work?
« Reply #6 on: 17/09/2008 20:26:11 »
Here is a simple explanation, by smiley .

Funniest thing I've seen for ages.

#### The Naked Scientists Forum

##### How does a Newton's Cradle work?
« Reply #6 on: 17/09/2008 20:26:11 »